# How many atoms are in 3.5 grams of silicon?

Mar 24, 2016

$= 7.505 \times {10}^{22}$ atoms. (rounded to third place of decimal)

#### Explanation:

Average atomic weight of Silicon, Si atom is $28.0855$ units.

We know from Mole concept that $1$ mole is $6.022 \times {10}^{23}$ of anything. This number is called Avogadro's number.

Also that $1$ mole of Silicon weighs $28.0855$ g.

Therefore,
$28.0855$ g of Silicon contains $6.022 \times {10}^{23}$ of Silicon atoms.
$3.5$ g of Silicon contains number of atoms $= \frac{6.022 \times {10}^{23}}{28.0855} \times 3.5$
$= 7.505 \times {10}^{22}$ atoms. (rounded to third place of decimal)